Turkey increased the number of warplanes patrolling its border with Syria after Tuesday’s downing of a Russian fighter jet following an alleged violation of Turkish airspace. The Turkish Air Force announced the intensified aerial protection Wednesday, saying the Syrian-Turkish border was now guarded by 18 F-16 fighter jets, according to Hurriyet Daily News.

Before the incident Tuesday, no more than 12 F-16s patrolled Turkish airspace. The move came in the wake of Russia’s statement that it would continue risky operations, including airstrikes, close to the Syrian-Turkish border, CNBC reported.

Turkey has contended the pilots of the Russian-made Sukhoi Su-24 fighter jet ignored repeated warnings after violating Turkish airspace, while Russia has maintained its jet was flying over Syrian territory.

The two Russian pilots ejected from the burning plane after it was struck by Turkish fighter jets. Russia said one of the crew members is apparently “alive and well” at a Russian air base in Syria, but his co-pilot was killed by gunfire as he parachuted from the jet, according to BBC News. It was not immediately clear what happened to his body. A video surfaced online Tuesday after the plane was shot down showing an apparently dead person purported to be one of the pilots.

Russian President Vladimir Putin has warned Turkey of “significant consequences” in the wake of the incident. Speaking ahead of his meeting with King Abdullah II of Jordan in Sochi Tuesday, Putin called Turkey “the accomplices of terrorists,” according to the Guardian.

NATO Secretary General Anders Fogh Rasmussen said Tuesday the alliance stands “in solidarity with Turkey and support[s] the territorial integrity of our NATO ally, Turkey,” before adding, “I have previously expressed my concern about the implications of the military actions of the Russian Federation close to NATO’s borders.”

Russian fighter jets first violated Turkish airspace during the country’s operations in neighboring Syria in October. At the time, NATO condemned Russian incursions into Turkey as representing an “extreme danger” and “irresponsible behavior,” Al Jazeera reported. Turkey joined the U.S.-led coalition against the Islamic State group in Syria in August, vowing to take on a more active role in the fight. Russia began its own airstrikes in Syria a month later.